The invention relates to a method of forming fixing heads on both ends of tension springs which are formed from coiled spring wire.
Many apparatus, in particular precision apparatus, require large numbers of tension springs whose ends are provided with eyelets. The eyelets are hooked onto fixing hooks and the like. During mounting, the springs are held by means of tweezers and first one eyelet is hooked into the appropriate fixing position, after which the spring is expanded and the other eyelet is hooked into the corresponding fixing position. This is an extremely time-consuming procedure. Moreover, there is a drawback in that the springs often escape from the tweezers during the hooking procedure and are catapulted far away. A further drawback consists in that the spring wire is greatly deformed by bending prior to the formation of an eyelet. This deformation often causes breaking of the spring wire at the area of deformation.
It is known (from U.S. Pat. No. 3,804,396) to form fixing heads on the expanded ends of a tension spring made of coiled spring wire. However, the nature of the formation of the heads is not accurately disclosed. Besides the fact that the tension springs provided with fixing heads in accordance with that United States Patent are straightened at their ends for the formation of the fixing heads so that they are susceptible to breaking, the described tension springs are used for safety belt fixings, so that they consist of an essentially thicker plastically deformable wire having a diameter in the order of magnitude of about 5 mm. The wire thicknesses used for precision mechanics are in order of magnitude of up to 0.8 mm.